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Fracture toughness tests were performed with 10 by 20-mm, deeply notched bend specimens of a mild steel and a nickel-chromiummolybdenum steel. Using the recently proposed J-integral test method, critical values of the energy line integral for Mode I crack growth, JIc, were determined for the two materials. The JIc results were discussed in relation to various specimen geometry criteria and critical crack growth criteria which have been proposed for a standardized JIc test procedure. The JIc results from the nickelchromium-molybdenum steel are found to be in excellent agreement with the known KIc value when the elastic deflection corresponding to the uncracked specimen is taken into account.
The JIc results from both steels are shown to be closely approximated by a one-specimen JIc test procedure, which is described and suggested for use as a fracture toughness screening test.
An analysis is presented of the error which arises in JIc determination when the effect of uncracked deflection in bend specimens is ignored. The error can be significant for materials with large values of yield strength relative to fracture toughness, even for deeply cracked specimens.
crack propagation, fracture properties, tests, compliance, steels
U. S. Army fellow, National Engineering Laboratory, East Kilbride,